Levothyroxine Dose Adjustment Calculator
This calculator tells you whether your current dose of levothyroxine (or any T4 thyroid medication, including Synthroid, Tirosint, Tirosint-SOL, Levoxyl, and Unithroid) needs to go up, stay the same, or come down based on your most recent TSH level. It’s built for patients already on thyroid medication who want a second look at their labs and an evidence-based recommendation for their next dose adjustment.
Pick your clinical scenario, pick your target TSH range, enter your TSH and current dose, flag any modifiers that apply, and the calculator gives you a recommended dose change along with the exact new dose in micrograms and the nearest commercially available tablet strength.
The calculator uses the same 12.5 to 25 mcg step-wise adjustment rules the American Thyroid Association and American Association of Clinical Endocrinologists recommend for hypothyroidism[1][2], with pregnancy-specific targets pulled from the 2017 ATA pregnancy guidelines[3] and cancer-specific TSH targets pulled from the 2015 ATA thyroid cancer guidelines[4]. It also offers Dr. Childs’ Optimal TSH range (0.5 to 1.0 mU/L) as the recommended default, which is tighter than the conventional lab range and closer to where most hypothyroid patients feel their best[6].
Note: This calculator is a decision-support tool, not a prescription. Dose adjustments should always be made with your prescriber. Don’t change your dose on your own, and never stop thyroid medication cold.
Most doctors use the wide conventional lab range. Dr. Childs recommends a tighter optimal range because that's where most patients feel their best.
TSH targets during pregnancy are tighter and change by trimester because your baby depends on your thyroid hormone, especially in early pregnancy.
Your endocrinologist assigns your risk level based on your cancer type, size, and how well it responded to treatment. Higher risk categories use TSH suppression to lower the chance of recurrence.
Written and medically reviewed by Dr. Westin Childs, D.O. Last reviewed: April 22, 2026.
How to Use This Calculator
Step #1: Pick Your Clinical Scenario
At the top of the calculator, pick the scenario that matches your situation: hypothyroidism (low thyroid), Hashimoto’s, thyroidectomy, partial thyroidectomy, subclinical hypothyroidism, pregnancy, or thyroid cancer.
The scenario sets the TSH target range the calculator will use to decide whether you need a dose change. Pregnancy and thyroid cancer both have their own sub-toggles that appear when you select them. Pregnancy reveals a trimester toggle (1st, 2nd, or 3rd), because the TSH target changes by trimester per the 2017 ATA pregnancy guidelines[3]. Thyroid cancer reveals a risk-stratification toggle (low, intermediate, or high), because TSH suppression targets are tied to cancer risk level per the 2015 ATA cancer guidelines[4].
If you’re not sure which scenario fits, pick “Hypothyroidism (low thyroid).” It’s the most common use case and uses the standard adjustment rules that apply to most thyroid patients.
Step #2: Pick Your Target TSH Range
For the non-pregnancy and non-cancer scenarios, the calculator gives you three target TSH ranges to choose from. The default (and my recommendation for almost every patient) is Dr. Childs’ Optimal range of 0.5 to 1.0 mU/L. This is a narrower target than the conventional lab range, and in my clinical experience it’s where the majority of hypothyroid patients start feeling well on thyroid medication[6]. Large epidemiologic data sets also show that the median TSH in truly healthy adults without thyroid disease is closer to 1.0 mU/L, which supports this narrower target[7].
The Functional Range (0.5 to 2.5 mU/L) is a middle-ground target often used by integrative and functional medicine providers. The Conventional Lab Range (0.45 to 4.5 mU/L) is the range most standard labs flag as normal. Using the conventional range means TSH values up to 4.5 are considered “in range,” even though many patients with a TSH of 3.0 or 4.0 still have hypothyroid symptoms.
For pregnancy, the target TSH is set by trimester. For thyroid cancer, the target is set by risk stratification. You don’t pick a general target TSH range in those two scenarios because the clinical guidelines are specific to those situations.
Step #3: Enter Your TSH, Current Dose, and Medication
Enter your most recent TSH value (in mU/L, which is the same as mIU/L), your current total daily dose of T4 medication in micrograms, and the specific medication you’re taking.
The medication dropdown includes generic levothyroxine, Synthroid, Tirosint, Tirosint-SOL, Levoxyl, and Unithroid, plus a generic “other T4 medication” option for patients outside the U.S. taking locally available T4 brands like Eltroxin, Euthyrox, or Thyrax. The medication you pick determines which tablet strengths the calculator rounds your recommended dose to.
For TSH, you only need the TSH value for this calculator to work. Free T4 and free T3 are useful clinically, but the dose adjustment math is driven by where your TSH sits relative to the target range you picked.
Step #4: Flag Any Modifiers That Apply
Three modifiers change how the calculator adjusts your dose: heart condition, age 65 or older, and ongoing symptoms.
Check the heart condition box if you’ve had a heart attack, heart failure, angina, or a history of arrhythmia. Age 65+ applies to anyone who is 65 years or older. When either of those is flagged, the calculator caps the dose change at 12.5 mcg per step instead of the usual 25 mcg, because rapid dose changes in these groups can trigger chest pain, palpitations, or arrhythmia.
The symptoms box is for patients whose TSH is technically in the target range but who still have hypothyroid symptoms (fatigue, brain fog, weight gain, cold intolerance, hair loss). When you check it, the calculator flags your result and reminds you that a “normal” TSH isn’t always enough, and that adding T3 or switching to natural desiccated thyroid (like Armour Thyroid or NP Thyroid) is often what makes the difference for patients with residual symptoms.
Understanding Your Results
TSH Status
The first thing the calculator tells you is where your TSH falls relative to the target range you picked: in range, above the upper limit, or below the lower limit.
A TSH above the upper limit means you’re undertreated and need a dose increase. A TSH below the lower limit means you’re overtreated and need a dose decrease. A TSH in range means the calculator will recommend no dose change, unless you’ve flagged ongoing symptoms, in which case the calculator will suggest the next clinical step (adding T3 or trying NDT).
Recommended Dose Change
The recommended dose change is the amount the calculator thinks your daily dose should go up or down, based on how far your TSH is from the target range. A small gap gets a 12.5 or 25 mcg adjustment. A larger gap gets a larger adjustment, up to 50 mcg per step for patients without cautious-dosing modifiers.
If you flagged a heart condition or age 65 or older, the step is capped at 12.5 mcg regardless of how far out of range your TSH is. The reasoning is simple: undershooting the target and taking a second adjustment in 6 to 8 weeks is always safer than overshooting and triggering cardiac symptoms in someone who is vulnerable to them.
Your New Total Daily Dose
This is the exact dose in micrograms that the calculator is recommending, before rounding to a commercially available tablet strength. It’s your current dose plus or minus the recommended step.
For example, if you’re on 100 mcg of levothyroxine and your TSH is 3.8 with a target of Dr. Childs’ Optimal range (0.5 to 1.0), the calculator recommends increasing by 25 mcg, giving you a new total daily dose of 125 mcg.
Nearest Commercially Available Strength
Because levothyroxine comes in specific tablet strengths, the calculator rounds your recommended new dose to the closest available strength for whichever medication you picked. Standard tablets (generic levothyroxine, Synthroid, Levoxyl, Unithroid) come in 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, and 200 mcg. Tirosint capsules add 13 mcg. Tirosint-SOL liquid adds 37.5, 62.5, and several other intermediate doses.
If your ideal new dose lands between two standard tablet strengths, Tirosint-SOL gives you the tightest possible match, since it comes in more increments than any other T4 product.
Scenario-Specific Notes
The last section of the results gives you clinical notes that change based on your scenario and modifiers.
For pregnancy, you’ll see trimester-specific TSH targets and the recommendation to recheck TSH every 4 weeks through the first half of pregnancy[3]. For thyroid cancer, you’ll see the TSH target for your risk level and the note that endocrinology follow-up is required[4]. For patients with a heart condition or age 65+, you’ll see a “start low, go slow” note. For patients with ongoing symptoms at an in-range TSH, you’ll see the suggestion to consider adding T3 or switching to natural desiccated thyroid.
TSH Target Reference Table
Here’s a quick-reference table of the TSH target ranges built into the calculator. The ranges below determine whether your TSH is considered in range, above the target, or below the target, and they drive the direction and size of the recommended dose change.
| Scenario | Target TSH Range (mU/L) | Source |
|---|---|---|
| Dr. Childs’ Optimal (recommended) | 0.5 to 1.0 | Clinical experience, supported by healthy-population TSH distribution[6][7] |
| Functional Range | 0.5 to 2.5 | Integrative / functional medicine target |
| Conventional Lab Range | 0.45 to 4.5 | Standard reference lab range[1] |
| Pregnancy, 1st trimester | 0.1 to 2.5 | 2017 ATA Pregnancy Guidelines[3] |
| Pregnancy, 2nd trimester | 0.2 to 3.0 | 2017 ATA Pregnancy Guidelines[3] |
| Pregnancy, 3rd trimester | 0.3 to 3.0 | 2017 ATA Pregnancy Guidelines[3] |
| Thyroid cancer, low risk | 0.5 to 2.0 | 2015 ATA Cancer Guidelines[4] |
| Thyroid cancer, intermediate risk | 0.1 to 0.5 | 2015 ATA Cancer Guidelines[4] |
| Thyroid cancer, high risk | Below 0.1 | 2015 ATA Cancer Guidelines[4] |
These ranges are all lower and tighter than the old reference range of 0.5 to 5.0 mU/L that was common before 2003. The National Academy of Clinical Biochemistry and multiple endocrine professional societies have since recommended a narrower normal range, closer to 0.4 to 2.5 or 3.0 mU/L, because more than 95% of disease-free adults have a TSH below 2.5[7].
If you’re on Armour Thyroid, NP Thyroid, Nature-Throid, or a compounded T3 medication, use the Thyroid Medication Conversion Calculator to find the equivalent levothyroxine-only dose before using this calculator. And if you’re not yet on any thyroid medication and you’re looking for a starting dose, use the Levothyroxine Dosage Calculator instead.
Frequently Asked Questions
A TSH above the upper limit of your target range means you’re undertreated and your dose needs to go up[1]. Which upper limit matters for you depends on your target. For most hypothyroid patients, the optimal upper limit is 1.0 mU/L. For pregnancy, the upper limit is 2.5 in the first trimester and 3.0 in the second and third. For thyroid cancer, the upper limit depends on your risk stratification.
In practice, a TSH above 2.5 mU/L in a non-pregnant adult on levothyroxine almost always calls for a dose increase, especially if symptoms are present. A TSH between 1.0 and 2.5 is a judgment call that depends on how you feel. A TSH above 4.5 is outside even the conventional lab range, and guidelines uniformly recommend increasing the dose.
Standard levothyroxine dose adjustments are made in 12.5 to 25 mcg steps, with 50 mcg reserved for patients who are significantly out of range and otherwise healthy[1]. A small gap from the target (for example, TSH of 2.5 with a target of 1.0) gets a 12.5 to 25 mcg adjustment. A larger gap (TSH of 8.0 with a target of 1.0) can justify a 50 mcg adjustment.
The step is capped at 12.5 mcg for patients with a heart condition or age 65 or older. Those patients are more sensitive to rapid changes in thyroid hormone and are more likely to experience chest pain, palpitations, or arrhythmia if the dose jumps too fast. Smaller steps with a recheck at 6 to 8 weeks is the safer approach.
In my clinical experience, the optimal TSH for most hypothyroid patients on levothyroxine is 0.5 to 1.0 mU/L[6]. That’s tighter than the conventional lab range (0.45 to 4.5) but reflects what actually correlates with symptom resolution in practice. Population studies of healthy adults without thyroid disease show a median TSH right around 1.0 mU/L, which supports targeting that range[7].
A TSH in the 2.0 to 4.5 range is technically “in the reference range” but is where a lot of patients still feel symptomatic on levothyroxine. If that’s you, a dose increase that brings your TSH closer to 1.0 is usually what resolves the symptoms. For the full breakdown, read my guide on optimal TSH levels for thyroid patients.
A normal TSH with ongoing hypothyroid symptoms is one of the most common problems I see in thyroid patients. The symptoms are fatigue, brain fog, weight gain, cold intolerance, hair loss, constipation, and depression, and they persist even though the lab result says you’re “in range.” This happens for two main reasons: the TSH target is too loose, or levothyroxine alone isn’t enough.
The first step is tightening the TSH target. A TSH of 3.0 or 4.0 is technically normal on the conventional lab range, but bringing it down closer to 1.0 often resolves symptoms. The second step, if symptoms persist at an optimal TSH, is adding T3 (liothyronine or Cytomel) or switching to natural desiccated thyroid (Armour Thyroid, NP Thyroid, or Nature-Throid). About 15 to 20% of hypothyroid patients have poor peripheral conversion of T4 to T3 and need T3 in their regimen to feel well[8]. For more on this, read my guides on adding T3 to levothyroxine and Armour Thyroid vs Synthroid.
Recheck your TSH 6 to 8 weeks after changing a levothyroxine dose[1]. TSH takes about 6 weeks to fully reflect a change in thyroid hormone levels, so checking earlier gives you a number that hasn’t stabilized yet. Acting on an early TSH can lead to over-adjusting the dose in the wrong direction.
Pregnancy is the exception. TSH should be rechecked every 4 weeks through the first half of pregnancy because thyroid hormone needs change quickly as the pregnancy progresses[3]. Thyroid cancer patients and post-thyroidectomy patients should follow the schedule their endocrinologist recommends, which is often more frequent than the 6 to 8 week standard.
If your TSH is 3.0 or 4.0 on levothyroxine and you have hypothyroid symptoms, yes, a dose increase is usually appropriate. A TSH in that range sits at the upper end of the conventional reference range, which means most labs will flag it as normal, but it’s also where many thyroid patients still feel undertreated. Large healthy-population data sets show the median TSH in disease-free adults is around 1.0, and more than 95% of healthy adults have a TSH below 2.5[7].
If your TSH is 3.0 or 4.0 and you feel fine, the decision depends on your provider’s philosophy. Standard endocrine practice often accepts anything within the conventional range. My preference is to bring TSH closer to 1.0 for symptomatic patients, and to reassess symptoms carefully for asymptomatic patients before committing to a dose increase. The calculator at the top of this page will tell you exactly how much to adjust based on whichever target range you pick.
During pregnancy, the TSH target changes by trimester per the 2017 American Thyroid Association pregnancy guidelines[3]. The targets are 0.1 to 2.5 mU/L in the first trimester, 0.2 to 3.0 in the second, and 0.3 to 3.0 in the third. These targets are lower and tighter than the non-pregnant normal range because elevated TSH in pregnancy is associated with miscarriage, preterm delivery, and adverse neurodevelopmental outcomes for the baby.
Levothyroxine requirements typically increase by 20 to 30% during pregnancy, and the increase usually needs to happen as soon as pregnancy is confirmed[3]. A practical way to make the adjustment is to add 2 extra doses per week (9 doses total instead of 7). TSH should be rechecked every 4 weeks through the first half of pregnancy, and the dose should return to pre-pregnancy level right after delivery with a TSH recheck at 6 weeks postpartum.
TSH targets after a total thyroidectomy for thyroid cancer are stratified by cancer risk per the 2015 American Thyroid Association guidelines[4]. Low-risk patients target a TSH of 0.5 to 2.0 mU/L. Intermediate-risk patients target 0.1 to 0.5. High-risk patients target a TSH below 0.1 (complete TSH suppression).
The reasoning is that TSH stimulates thyroid tissue growth, including any residual cancer cells. Suppressing TSH reduces the risk of cancer recurrence, but it also increases the risk of overtreatment side effects like atrial fibrillation and bone loss over time. The risk-stratified approach balances these two concerns. Post-thyroidectomy cancer patients should always be managed with endocrinology follow-up, and the calculator above is a decision-support tool, not a substitute for that relationship.
Signs that your levothyroxine dose is too high look like mild hyperthyroidism or thyrotoxicosis: fast or irregular heartbeat, palpitations, anxiety, insomnia, hand tremor, heat intolerance, increased sweating, unintentional weight loss, loose stools, and irritability. A TSH below 0.3 mU/L (when TSH suppression isn’t the clinical goal) confirms it.
Long-term overtreatment has real risks beyond discomfort. A suppressed TSH over months to years is associated with atrial fibrillation, accelerated bone loss, and osteoporosis, especially in postmenopausal women and older adults. If your TSH is below your target range, the calculator will recommend a dose decrease. For more on the symptoms, read my guide on Synthroid and levothyroxine side effects.
Patients with heart disease and adults over 65 are more sensitive to rapid changes in thyroid hormone[1]. A sudden 25 or 50 mcg jump in levothyroxine can trigger chest pain, palpitations, or arrhythmia in someone with underlying coronary artery disease, heart failure, or a history of atrial fibrillation. Older adults clear levothyroxine more slowly and have a higher baseline risk for cardiac side effects even without a known heart condition.
The calculator caps the dose change at 12.5 mcg per step for those groups. The tradeoff is that you may need two adjustments instead of one to fully correct the TSH, but that’s always safer than overshooting. Recheck at 6 to 8 weeks, and if the TSH is still out of range, take another 12.5 mcg step.
This calculator is built for T4-only medications (levothyroxine, Synthroid, Tirosint, Tirosint-SOL, Levoxyl, Unithroid). If you’re on Armour Thyroid, NP Thyroid, Nature-Throid, or WP Thyroid, those are natural desiccated thyroid (NDT) products that contain both T4 and T3, and the dose adjustment math is different.
To use this tool if you’re on NDT, first convert your NDT dose to its levothyroxine-equivalent using the Thyroid Medication Conversion Calculator, then run that equivalent through this calculator to see what direction your dose should move. The T3 component will complicate things, so NDT dose changes should always be made with a provider familiar with these medications. For the basics, read my Armour Thyroid vs Synthroid comparison.
References
- Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014;24(12):1670-1751. View on PubMed
- Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocrine Practice. 2012;18(6):988-1028. View on PubMed
- Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017;27(3):315-389. View on PubMed
- Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2016;26(1):1-133. View on PubMed
- Peeters RP. Subclinical Hypothyroidism. New England Journal of Medicine. 2017;376(26):2556-2565. View on PubMed
- Childs W. Optimal TSH level for thyroid patients on thyroid medication. restartmed.com. Read article
- Hollowell JG, Staehling NW, Flanders WD, et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab. 2002;87(2):489-499. View on PubMed
- Wiersinga WM, Duntas L, Fadeyev V, Nygaard B, Vanderpump MP. 2012 ETA Guidelines: The Use of L-T4 + L-T3 in the Treatment of Hypothyroidism. European Thyroid Journal. 2012;1(2):55-71. View on PubMed